Kept quiet and booked (9)
I believe the answer is:
preserved
'kept' is the definition.
(preserving is a kind of keeping)
'quiet and booked' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano').
'and' says to put letters next to each other.
'booked' becomes 'reserved' ('reserve' can be a synonym of 'book').
'p'+'reserved'='PRESERVED'
(Other definitions for preserved that I've seen before include "Kept safe from harm" , "Prevented from decaying or spoiling" , "Prevented from decay" , "Maintained in an unaltered condition" , "Kept in an unaltered condition" .)